The present embodiments relate to a medical imaging unit having a tomography device for 3D imaging and having a PET system for positron emission tomography.
DE 103 39 493 discloses a PET-CT scanner. US 2003/0014132 discloses a PET unit.
During positron emission tomography (PET), a patient is injected with a tracer, such as 18F-FDG (fluorodeoxyglucose), by mixing a radionuclide that has a comparatively short half-life with a carrier substance. The tracer accumulates in certain organs and cellular tissues and decomposes, emitting positrons. The enrichment may occur in active cancer cells.
After a relatively short distance, typically 1 mm, a positron liberated (emitted) in the process of radioactive decomposition interacts with an electron, whereupon both particles are destroyed and two gamma quanta, with an energy of 511 keV each, are emitted in diametrically opposite directions. These annihilation quanta may be proven to exist with spatial and chronological resolution in a detector ring, surrounding the object of the examination, such as the patient. The ring includes one or more gamma detectors located adjacent one another that may be read out individually. By means of coincidence collimation in an electronic evaluation unit behind the detectors, the site of the electron-positron annihilation, on which the counter events are each based, may be ascertained along the imaginary line between the signal-emitting detector elements, known as the line of response. The emission of the gamma radiation takes place isotropically. All the directions of emission of gamma radiation, statistically, are equally probable. From a statistically significant large number of counter events, the spatial frequency distribution of the radioactive decomposition processes and the distribution of the tracer in the body may be derived. From this kind of 3D volumetric data set, arbitrary two-dimensional PET slice images may be generated.
PET is a functional imaging process that may reproduce and display biochemical and physiological processes in the organism. PET provides analysis of the metabolism. PET may be used to find tumors and metastases and to assess perfusion of the heart muscle. PET has a local resolution (approximately 5 mm), which generally cannot be increased without additional radiation exposure. PET does not provide good anatomical images, and thus the spatial localization and association of the loci of disease found presents difficulties.
The combination of PET and CT scanners is becoming increasingly popular, especially in radiation therapy. The tracers injected in a PET examination accumulate in tumors and metastases, for example, and thus make the tumers and metastates easier to locate. A CT scanner provides anatomical information, and the PET unit provides functional information, for example, about cellular activities and metabolic processes in a target volume. In combination, both geometric and functional information about the turner or metastates may be used for determining the target region, when planning for radiation therapy.
DE 10 2005 048 853 discloses a combination of a PET unit with a 3D X-ray system, such as a cone beam CT scanner. The PET unit and the 3D X-ray system are, for example, located side by side, so that a patient lying on a patient examination or treatment table may be moved in succession to the two imaging units.
For radiation therapy, the same patient mount may be used both in radiation planning and for the radiation; for example, structurally identical patient mounts are used. Using the same patient mount increases the precision in radiation therapy, since mechanical imprecision's are the same in both cases.
In PET-CT combination units in the prior art, in particular robotic patient positioning units, which have an engagement point of the support arm below the stretcher, for instance, cannot use the same patient mount. The support arm would collide with the “front” imaging units when the patient is moved into the “rear” imaging unit. Thus, there is a need for a combination unit with stretchers and patient positioning units that may be used for radiation planning and for the radiation itself.